1. Field
This invention relates to black powder guns and provides improved manufacturing techniques and components. Specifically, this invention provides a means for incorporating improved technology in black powder guns which retain traditional styling and function. More specifically, this invention pertains to a composite breech plug of the full hook type and manufacturing methods involving its use.
2. State of the Art
There has recently been a resurgence in the popularity of black powder guns, particularly smooth bore and rifled stocked guns. Modern enthusiasts of black powder guns generally desire pieces of traditional styling and action. Traditionally, high quality black powder guns have included a full hook breech plug adapted to interlock with a tang carried by the stock. The traditional black powder gun barrel is octagonal and the same octagonal pattern is carried through the exposed portion of the breech plug and tang. It is imperative, from an esthetic standpoint, that the flats of the exposed portion of the breech plug match the external flats of the remainder of the barrel, that the barrel breech end and breech plug be aligned, and that the breech plug flats and hook be aligned with the tang.
The conventional method of fitting a breech plug to a black powder gun is to first manufacture a one-piece plug. Such a plug includes a threaded extension, adapted for insertion into the barrel, and a main body, adapted to extend to the rear of the barrel. The main body includes external octagonal flat sides, and a full hook projecting from its rear surface (tang face). The threaded extension is screwed into a counter bore at the breech end of the barrel until the flats on the breech plug and barrel, respectively, are precisely lined up with each other and a gas seal is developed between the breech plug and barrel. It has been necessary to time the external threads of the plug with the internal threads of the barrel. Otherwise, when the flats are properly aligned, either (1) the breech plug may not be seated with sufficient torque to develop a proper gas seal or (2) unacceptable stresses may be developed at the notch point created by the threads of the plug, since those threads are in tension.
It is important that the plug create both a shoulder match line and a bore seal. By "match line" is meant that the flats of the barrel are in registration with the flats of the main body of the breech plug. The bore seal is effected at the interface between the forward end of the breech plug and the counter bore of the barrel. The shoulder match line is effected at the extreme breech end of the barrel at the interface between the barrel and the breech plug. It has been necessary to hand qualify one or the other of these surfaces to meet the standards of quality arms. In practice, hand qualification is so expensive that it is only performed in the case of very expensive firearms. Accordingly, the usual practice is to accept a small gap at the bore in production rifles.
Several problems are commonly encountered with breech plugs turned to effect a shoulder match line while aligning the flats (creating a match line). The threads are inherently put in tension. Accordingly, stress is translated to the notch point at the threaded extension of the plug. Firing the gun puts additional force on this notch area, which may cause the plug to fail. In addition, gases tend to blow back through the threads because of the lack of a proper bore seal, causing erosion and further weakening at the notch point. Eventually the shoulder seal can be eroded away. Moreover, the threads are often destroyed so that it is not practical to remove the plug from the barrel, which defeats the initial purpose of a quality full hook breech gun. Another dangerous condition develops as unburned residue accumulates in the gap at the bore. This residue creates a "fire ring" which can causes preignition of a fresh charge of powder.
The conventional method for making gun barrels also inherently causes difficulties in fitting a full hook breech plug. Normally, the barrel is drilled from its muzzle end, and the drill inevitably runs out at the breech with a tolerance of about 0.001 per inch of barrel length. Accordingly, in a 30 inch barrel, the caliber bore may be 0.030 inches off center at the breech end. This "bore run-out" is random, and makes it impossible to use standard breech plugs. Two methods have been used to fit breech plugs to barrels of random bore run-out, both of which are quite expensive. The first of these is to install the breech plug and then mill the external flats and tang hook on the breech plug with reference to the flats and breech end on the barrel. The other method is to drill an oversized barrel blank and then machine the barrel flats with reference to the previously drilled hole.
The high cost of machining operations necessitates that present day techniques for producing breech plugs include investment casting. Investment cast breech plugs oftentimes have structural defects that would cause them to fail in use, particularly in the area where the threaded extension joins the main body. Therefore, they are routinely x-rayed so that bad castings may be rejected. Also, secondary machining of timed threads, and selection of casting metals for strength properties and heat treating characteristics is quite expensive.
In summary, there has been a longstanding need for a breech plug assembly and fitting procedure which avoids the annoying, costly, and dangerous problems of the prior art while providing high quality black powder firearms. There is also a need for increased interchangeability of parts.